1. Field of the Invention
The disclosure relates to an ossicular prosthesis used for total replacement and reconstruction of the ossicular chain. More particularly, the disclosure relates to an adjustable length ossicular prosthesis.
2. State of the Art
Due to disease, trauma, or congenital malformation, the ossicles of the middle ear are sometime damaged. If this damage results in a discontinuity of bone between the tympanic membrane and the oval window, no sound conducts and hearing loss results. Some or all of these ossicles can be replaced with a small prosthesis. The material of choice for many years has been and, for some surgeons, continues to be the patient's own bone. Usually, the incus body will be harvested and reshaped into a strut that bridges whatever gap exists between the tympanic membrane and the oval window. Although this is an effective method of reconstruction, the time required to harvest and sculpt the incus bone into a usable prosthesis has led to the development of synthetic replacements.
Plastic prostheses used for reconstruction of the ossicular chain have been used for some time. A total prosthesis is generally shaped like a nail or tack and replaces all of the ossicles (malleus, incus and stapes) of the middle ear. A partial prosthesis replaces the malleus and the incus. This prosthesis is similar in shape, but has a hollow cylinder for the reduced portion of the prosthesis. The hollow cylinder fits over the head of the stapes. Plastic prostheses generally require a disc of cartilage be placed between the head of the implant and the tympanic membrane. These discs are harvested during surgery. The disc prevents the implant, in most cases, from eroding the tympanic membrane and becoming dislodged over time “extruding”.
Subsequent developments have provided movable joints to allow angular adjustment or bendable wire cores. Such joints allow the orientation of a implant to be fixed or set at the time of implantation to match the anatomy.
For each type of ossicular prosthesis, several lengths have generally been provided given the natural differences in anatomical distances between middle ear structures in different patients. This required that a device company manufacture, and that a surgeon (or medical facility) inventory, various sized prosthesis to accommodate the variations in dimensions across the anatomy of patients.
In response, co-owned U.S. Pat. No. RE40,853 discloses an adjustable length prosthesis for ossicular replacement or reconstruction. The disclosed prosthesis is sold by Grace Medical under the trademark ALTO. The ALTO prosthesis includes a head for contacting a tympanic membrane, with the head having a through opening. An elastomeric sleeve is mounted beneath the head at the through opening. The elastomeric sleeve includes a through opening coaxial with the head through opening. An elongate shaft has a near end extending through the sleeve through opening and then the head throughbore. The elastomeric sleeve throughbore is adapted to grip the shaft under static conditions but permit the shaft to move axially to adjust shaft length during the implant procedure. The distal end of the shaft includes structure for contacting a footplate or stapes when implanted in a human ear. The shaft is plastically bendable to accommodate angulation for better anatomical fit. The shaft is received in the head and trimmable with a scissors or scalpel to adjust the length of the prosthesis.
While the ALTO prosthesis works well, the combination of the head and flexible sleeve limit the amount of lengthwise adjustment permissible to the prosthesis prior to implant. In addition, it has been identified that due to ambient or dynamic changes in pressure within the middle ear after implantation, e.g., by sneezing or high sound pressure levels (SPL) caused by an intense noise, the distance and orientation between prosthesis coupling points can temporarily change. This situation may result in dislodgement of the prosthesis or otherwise lead to poor sound conduction along the ossicular chain.
Further, the construction of the ALTO restricts the minimum length to which the prosthesis can be adjusted. For patients with small anatomical spacing between the tympanic membrane and footplate or stapes, such restriction can be a limitation on use of the ALTO prosthesis.